I go along with Krochus somewhat, except for the barrel prices and if it is home grown rather than custom done. I just did a SMLE...90 bucks Midway barrel, and a VZ24 Lothar Walther barrel, 219 bucks, threaded, chambered and crowned, ready to screw on and shoot, but what he said about Mauser conversions is totally true...and totally oldhat. Time consuming, lots of mucking about, special tools and jig to make or buy and not for the faint of heart or the beginner unless you have lots of patience...fun tho'.
I just bought a beautiful Mauser Modelo Argentino 1891 manufactura Loewe, Berlin...86 bucks including background check cost...yesterday (Fri). Bore is perfect, 95% on the rest, crest groundoff on the receiver but that is almost always true, all pieces same number, stock was sporterized and bolt bent, but excellent job...a very nice shooter...old world craftsmanship to the max...a few "character marks" on the stock and one burrheaded screw and a bit of cosmoline still in the bolt recess.
This caliber is as close to a 308 as you can get without being one...of course it has a 0.311" bore, same as the 303 Brit. Midway has PRVI ammo available, 180 gr bullet 2542 fs/2588 ft lbs, but otherwise you have to make cases out of '06 or x57 brass or pay Norma prices. Easy enough for those that have the tools and desire, dies are also available around 30 dollars at Midway...my Lee set is on it's way along with 2 boxes of PRVI ammo and I have plenty of 8mm brass if I need to make more cases.
I WOUDN'T re-barrel mine...this action is rated in the 52 KPSI range (Norma Ammo), only two bolt lugs and no third safety lug...it has been pushed to higher pressures tho', lots of re-barrels done in the past, but the rifle as is, drilled and tapped for scope mounts will kill any NA game including bears although I want something much bigger for the mean and nasty's. AND the magazine is a strange contraption, it will function with the ammo it was designed for absolutely and perfectly and those similarly shaped, but otherwise there is another costly expense to modify it for something else that won't work as good. I could see re-barreling to something built on the 308 or shortened x57 cases like a 6mm, 6,5mm, 7mm, 338 Fed, or a 358 Win, maybe a 9.3(I would stop there as the muzzle is 0.600" O.D.), or you could have one of the re-borers do it, although I can't see any reason to mess with a perfectly good cartridge.
This rifle is one of those silk purse/sow's ear things. My rifle is a silk purse and doing ANYTHING to it would turn it into a sows ear quick time.
Considering the prices of these rifles, I'm not sure I would be very fond of a uncle trying to work me unless this rifle happens to be perfect in all respects AND in the collectors realm.
The 1891 Argentine, sometimes called the Belgiun or Spanish mauser, has always been a 7.65x 53mm caliber. The 1909 Argentine came out much later and is a M98 action and came in several different calibers over many years, makers, countries and wars. Lots of confusion in the nomenclature of the Mausers...I'm still wading throught the "stuff" trying to get some kind of handle on the different models, sizes and interchangeability of the parts.
Good luck.